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  • Decomposers
    • as plants and animals, live they excrete material such as carbon dioxide and urea which are returned to the environment in waste or they egest material in their faeces
    • many trees shed their leaves each year
    • The Process of Decay
      • carried out by microorga-nisms such as saprophytic bacteria and fungi
        • they secrete extracellular enzymes which digest the large and complex molecules in the dead and decaying matter and break them down into small, soluble molecules which they can absorb e.g. glucose
        • when these saprophytic bacteria and fungi respire, they use the glucose they have absorbed and release carbon dioxide which can be used by plants in photosynthesis
          • this is an example of how decomposers recycle chemical materials from the bodies of dead organisms
      • this process is vital in recycling chemical materials and allows them to be taken up again by plants
        • the nutrients are then passed on to animals when they eat the plants
          • if all the materials weren't eventually recycled and returned to the environment, some would run out
      • in a stable community the processes that remove materials are balanced by the processes that return materials
    • Conditions for Decay
      • moisture - decomposers need a certain amount of moisture to help them dissolve their food
        • the moisture also helps them to grow better because it prevents them from drying out
      • optimum temperature - chemical reactions in microbes are controlled by enzymes and work faster in optimum conditions
        • if the temperature is too high the enzymes will be denatured and the chemical reactions controlled by them will stop irreversibly
        • if the temperature is too low, the chemical reactions will not have enough energy and begin to slow down and may stop
      • oxygen - decomposers are microorgan-isms. like all living organisms they need to respire aerobically in order to release energy for growth and reproduction.
        • most decomposers require oxygen for aerobic respiration and so decay will take place much faster if it is present
      • large surface area in the decomposingmicroorgan-ism - ensures rapid diffusion of digested material into the bacterial cell or fungal hypha
    • the importance of decay in recycling
      • humus is the organic content of the soil formed from decomposing plant and animal material
      • it is rich in mineral ions and molecules released from the extracellular digestion by enzymes secreted by saprophytic bacteria and fungi
      • it provides many nutrients for plant growth
  • The Decay Process
    • waste, dead and decaying matter are eaten by detrivores e.g worms They shred the material up into very small pieces and produce waste material
      • saprophytic bacteria and fungi digest everything. the bodies of dead animals, plants, detritus feeders and waste they produce are all broken down by decomposers and recycled in their:
        • waste - HUMUS
          • minerals returned to soil which plants can absorb and need to grow .g. magnesium for chlorophyll formation
        • growth and reproduction
          • new decomposer material e.g. amino acids for protein formation
        • respiration
          • carbon dioxide which plants can use in photosynthesis to form glucose


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